After breaking early in the third set, Sevastova looked to have climbed back into the contest after an epic sixth game.

The Latvian needed six break point opportunities but eventually prevailed, only to be broken back in the very next game.

Osaka thumped a mammoth 51 winners compared to just 22 from Sevastova.

The aggression and power was the clear difference between the two players, with Sevastova seeming to go more into her shell and becoming more defensive as the match became closer in the defining set.

"For me today, I feel like during the first set, I might have tried to overhit or she was returning a lot of balls. So I thought I had to go for more than I did," Osaka said.

"In the second and third set, I calmed down and I tried to think that I should play within my boundaries. So, yeah, it is a little bit natural, but unnatural at the sametime."

Osaka will now play sixth seed Elina Svitolina, after the Ukrainian defeated American Madison Keys in three sets.

The topsy-turvy affair saw Svitolina win the first set 6-2, before Keys won the second set 6-1 in just 23 minutes.

Despite the American hitting 37 winners to 22 in the match - including 26 on her forehand - Svitolina wasn't to be denied and won the third and defining set 6-1.

It ends a poor run of results in majors against top-20 players for the Ukrainian, with Svitolina losing her last six matches against them.

Ukraine's Elina Svitolina celebrates her victory after American Madison Keys.Credit:AP

Her previous win against a top-20 player dates all the way back to the 2016 French Open, when she defeated Ana Ivanovic.

Svitolina has been in three grand slam quarter finals before without success, but the 24-year-old said she won't be thinking about the past as she attempts to reach her first major semi final.

"I only look forward. I look for the next challenge. I try to win as many matches as I can, as many titles as I can, and this is the goal for the year.

"So far I think I have been serving really good. I have been returning solid. So, you know, I always try to put pressure on the opponent.

"That's why I think, yeah, I'm in quarter-final because I have been solid in all the matches."

In the other fourth-round match on Margaret Court Arena, seventh seed Karolina Pliskova had little trouble in brushing off 18th seed Spaniard Garbine Muguruza, winning in straight sets 6-3, 6-1 in just under an hour.

Pliskova won 82 per cent of points on her first serve and incredibly hit only three unforced errors to Muguruza's 20, helping her storm into her third Australian Open quarter-final.